Vehicle handling and stability have been important areas of research for quite some time due to an increased focus on traffic safety and because of customer demand. Two common types of unstable conditions that a vehicle, such as a car, may encounter are referred to as oversteering and understeering. Oversteering is the situation where the rear end of the vehicle moves towards the outside of a turn instead of following the curvature of the turn. Understeering is the opposite situation where the front end of the vehicle moves towards the outside of the turn instead of following the curvature of the turn.
There exist several ways of controlling the vehicle in order to counteract an oversteer or an understeer condition. For example, a torque vectoring mechanism may be used to distribute a torque between a left and a right rear wheel and in this way counteract the understeer or oversteer condition. More specifically, if the vehicle is subject to understeer in a turn, the torque vectoring mechanism may be controlled to increase the torque on the outer rear wheel. Conversely, if the vehicle is subject to oversteer in a turn, the torque vectoring mechanism may be controlled to increase the torque of the inner rear wheel.
A general problem with using torque vectoring mechanisms for improving stability of a vehicle is that the understeer or oversteer condition may grow worse if too much longitudinal force is applied to the wheels coupled to the torque vectoring mechanism. In a case where the torque vectoring mechanism is coupled to the rear wheels, an oversteer condition may be aggravated. This is due to the fact that as a driving force or a torque is applied to the rear wheels, the lateral force capacity of the rear axle decreases and at some point the lateral force capacity of the rear axle saturates. As a result, the oversteer condition gets worse, decreasing the stability of the vehicle. In a case where the torque vectoring mechanism is instead coupled to the front wheels, an understeer condition may be aggravated. Similarly to the case of the rear wheels, as a driving force or torque is applied to the front wheels, the lateral force capacity of the front axle decreases and at some point the lateral force capacity of the front axle saturates. As a result, the understeer condition gets worse and the stability of the vehicle decreases.
There is a need for a method for controlling a torque vectoring mechanism, as well as a torque vectoring system, that provides improved performance.